An ambulance responding to a two-vehicle collision in northwest Denver was hit by a third vehicle Thursday. Two victims from the initial accident were in the ambulance at the time.

The incident happened about 12:35 p.m. at the intersection of West 8th Avenue and Federal Boulevard, said Sonny Jackson, a Denver Police Department spokesman.

Two people, an adult and a child, suffered serious injury and were inside an ambulance. The ambulance was pulling away from the scene when it was hit by a third vehicle , said Cindy Matthews, a Denver Health Medical Center spokeswoman.

The ambulance was hit on the front passenger side. No one in the vehicle that hit the ambulance was injured, Matthews said.

Since both people in the ambulance were seriously injured in the initial accident, the ambulance proceeded to the hospital. It returned to the scene after dropping off the pair.

Two other people, both adults, in the initial accident were also taken to Denver Health in a second ambulance. Details on their injuries were not available. A third ambulance was sent to the scene, but it did not transport anyone.

Traffic investigators with the police department are working on the incident.

Kieran Nicholson covers breaking news for The Denver Post. He started at the Post in 1986, at the old building on 15th and California streets. Nicholson has covered a variety of beats including suburbs, courts, crime and general assignment.

Colorado energy regulators on Monday proposed tighter rules for shutting down oil and gas pipelines after a fatal explosion blamed on natural gas leaking from a line that was thought to be out of service but was still connected to a well.